Push-button-operated coding systems are known, for example the encoding of telephone numbers by push-button phones. Copending, cross-referenced and herein incorporated application Ser. No. 864,742, filed Dec. 27, 1978, Horst WILLACH in which the coding circuit is so arranged that single or multiple operation of selected ones of a group of a push-buttons provides pulses, associated with the respective value or digital position assigned to a specific push-button and which is, in turn, associated with a certain position of a combination. The circuit additionally is connected to a source of energy which provides electrical energy to permit an opening operation of the lock to be carried out, for example by pullin-in a magnet which otherwise blocks or prevents opening operation of the lock, for instance by a knob. The energy source is time-limited to provide electrical energy only for a predetermined time interval or, rather, for a predetermined amount of energy, which is charged upon operation of the first push-button in accordance with the coded combination. After a predetermined time interval, as determined by the time element, the coded circuit is deenergized, resulting in automatic locking of the locking mechanism.
The timing circuit and energy supply circuit in accordance with a feature of the cross-referenced application in its simplest form is a capacitor which is charged from a source of electrical energy, the charge on the capacitor then supplying the necessary electrical energy for both the decoding of the push-button operation and for initiating permission of the unlocking of the lock, for example by pulling in a magnet for a predetermined and limited time interval.